Direction finder or omnirange beacon with wide-aperture antenna system



1954 FRITZ STEINER 3,144,649

ALSO KNOWN AS FRIEDRICH STEINER DIRECTION FINDER OR OMNIRANGE BEACON WITH WIDE-APERTURE ANTENNA SYSTEM Filed June 26. 1959 7w Trans ducer Fansducer INVENTOR.

FT F STEINER United States Patent O 3,144,649 DIRECTION FENDER OR OMNIRANGE BEACON WITH WIDE-APERTURE ANTENNA SYSTEM Fritz Steiner, also known as Friedrich Steiner, Iforzheim, Germany, assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed June 26, 1959, Ser. No. 823,196 Claims priority, application Germany July in, 1958 6 Claims. (til. 343-106) The present invention relates to an antenna system and more particularly to a wide apertured antenna system used as a direction finder or as an omnirange beacon.

One problem, frequently arising with direction finders or omnirange beacons relates to the removal of bearing errors which are due to disturbances in propagation, such as multipath propagation. As is well known, this is accomplished by using a so-called wide-aperture antenna system in which the direction-finding accuracy, by taking the mean in a disturbed interference field of the radio waves, is increased.

Earlier proposed beacon systems using an antenna system of wide aperture, such as Consolor, bear the disadvantage of bearing errors being produced to ambiguity, which can only be removed by considerable expenses or by employing another navigational aid to compensate for these errors. An explanation of this system is referred to in the book entitled Radar and Electronic Navigation, by G. I. Sunnenberg, pages 114 to 136. On the other hand, systems have also become known which operate on the principle of amplitude modulation with wide aperture antenna systems, such as the direction-finding system known by the name of Wullenweber, which provides unambiguous bearing information. In this direction-finding system a Very narrow lobe, produced by combining several antennas, continuously rotates round a ventical axis. However, due to the very narrow lobe pattern, this system requires at the receiving end a substantially broad band AM-receiver.

In addition several other direction-finding systems have been proposed operating on frequency-modulation or phase-modulation principles. When employing antenna systems of wide aperture, it was found that they are capable of avoiding bearing errors due to ambiguity. To compensate for these errors specific types of FM-modulating receivers employing more antenna elements must be used, resulting in a more expensive AM-receiver.

In the fields of omnirange radio beacons or directionfinders there will often arise the problem of converting transmitting and receiving equipments, operating with rotating directional diagrams, such as cardioid patterns (limacon patterns), into systems employing an antenna system of wide aperture. This should be accomplished by making a minimum of changes in the present equipment.

The present invention now provides a way for solving this problem. According to this invention the interference field of the radio waves are periodically scanned within a range which is large with respect to the operating wave-length. A directional pattern, such as a cardioid (limacon pattern), which is aligned in a radial direction with respect to the center of rotation of said antenna elements, then rotates round a point lying several wavelengths away from the origin of the cardioid. In this 3,144,649 Patented Aug. 11, 1964 ice way there is created what is called a site or space diversity, so that a mean value of the bearing can be formed Within the distorted interference field of the radio waves produced by the multi-path propagation. During the rotation of this directional diagram on a circle, a phase modulation of the wave is produced. It should be remembered that this phase modulation is to be neglected in the case of a slow rotation.

At the output of the receiver the rotating diagram will result in an envelope of a sinusoidal alternating-current voltage from which the bearing information can be obtained in the conventional manner by means of a phase comparison with a fixed-phase reference signal.

Other possibilities for realizing the production of such a direction diagram will be explained hereinafter.

The substantial difference which is due to the fact that the antenna array rotates eccentrically instead of rotating round its origin of radiation, consists in that the antenna arragement, on its rotation path, successively samples the entire distorted interference field of radio waves caused by the multipath propagation, whereby a mean value between the individual bearing information, deviating by that particular value corresponding to the direction of incidence of the stronger wave, is found. In this type of arrangement a kind of site or space diversity is created.

Without necessitating a modification of the receiving equipment, the system as described herein may be used to improve the conventional VOR-beacon system by merely altering the antenna system of the transmitter in accordance with the principles of the invention. In this way there is obtained an omnirange beacon having all the advantages of a wide-aperture antenna system, and the added advantage that erection site of the system can be chosen independently of the respective terrain. With respect to the VOR-systems which are in operation at present, the erection site has to be selected very carefully in order to avoid a multipath propagation of the waves, which can result in the aircraft being provided with faulty bearing information. The same principle may be applied in the same way to amplitude direction finders using smallaperture antenna systems. Thus, a much more exact evaluation of the bearing information is achieved by using the wide-aperture system.

The above-mentioned and other features and objects of the invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings in which:

FIG. 1 shows a wide aperture antenna utilizing a single circular arrangement of antenna means, and

FIG. 2 shows a wide aperture antenna system utilizing two concenrtic circular arrangements of antenna means.

FIG. 1 illustrates an antenna arrangement for producing a rotating cardioid pattern (limacon pattern) with one single circular arrangement of antennas which can be obtained with the use of a retardation element L (which is a cable section of the length V4), rotating together with the switch. One antenna then effectively becomes a radiator and the following one a reflector. One end of the cable length L which rotates together with the switch, is connected to the input of a transducer. As a switch there may be used the already proposed capacitively coupled switch, as described in my copending application Ser. No.

794,014, filed February 18, 1959, now Patent No. 3,048,- 843.

For enabling simultaneously a transmission of information by speech, and by employing the principle of the invention, there is chosen at the receiving end of a system a small modulation factor of the wave. In addition thereto the speech quality can be improved to a certain degree in the conventional manner by means of speech recovery techniques.

However, in further embodying the invention and for ensuring unobjectionable intelligibility, the bearing information is modulated to a subcarrier whose frequency is substantially higher than the highest frequency of the speech band to be transmitted.

According to a further embodiment of the invention the problem of providing unobjectionable speech transmission can also be solved by connecting two antennas to each other by means of a rotating length of cable. The connecting point of the receiver, which could be the two ends of the cable length or the foot points of the antennas S, FIG. 1, is then switched over with a substantially higher frequency than corresponds to the rotation frequency of the directional diagram. On account of this the bearing information will appear as a carricrless modulation of the switching frequency and may be separated and evaluated in the conventional manner. Referring to FIGURE 1, the reference S is a mechanically or capacitively coupled switch by which either one of a pair of adjacent antenna elements (e.g. i or 2) is directly coupled to the transducer. To this end, one position of the movable arm of the switch is symbolized by a dotted arrow and the other by a solid arrow. The result is that the position of the cardioid pattern formed by combining antenna elements 1 and 2 by means of a delay line L positioned between contacts and a and b of switch rotor, is reversed from the position shown in FIGURE 1 by a solid line to the position shown by a dotted line.

Another embodiment to create a cardioid pattern is shown in FIGURE 2 wherein antenna elements 8 and 9 are positioned on concentric circles 10 and 11 respectively at a predetermined radial spacing so that by combining active antenna element 12 and passive antenna element 13 radially positioned with respect to one another (14 and 15 and so on), a cardioid pattern is created by each two elements 12 and 13, etc., positioned with respect to the circles 10 and 11 as shown in FIGURE 2, said cardioid pattern revolving on a circle around the array.

This problem may also be carried out in the case of a rotating antenna where two reflectors are rotating on both sides of the antenna. These antennas are alternatingly switched with a switching frequency lying above the speech frequency. In this case the bearing information will then exist as carrierless modulation of the switching frequency at the output of the receiver, and two very different frequencies, such as 25 c.p.s. and 5000 c.p.s. may easily be separated by means of filters.

There is still conceivable another embodiment of the idea of the invention, in which there is used or employed a pilgrim step motion of one individual antenna element on a straight line (linear antenna array), such as described in the aforementioned copending application, which may be realized either mechanically or electronically. Thus to the respective antenna elements, as seen from the direction of motion, there is assigned a reflector alternatingly in front and behind the antenna. In this way there will be obtained an amplitude modulation, whose modulation factor, or whose amplitude after the demodulation will correspond to the sine of the angle of incidence of the radio waves.

By employing such linear antenna arrays, crossing each other at an angle of e.g. 90, there will be obtained in the case of a simulated motion of the antenna with the associating reflectors from the one linear antenna array, the sine, and from the other the cosine of the angle of incidence of the radio waves, which is combined in the conventional manner in a display, for the purpose of being indicated.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention, as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

l. A directional radiant acting circuit in a form of a circular array of antenna means, comprising a transducer, and means for cyclically coupling adjacent antenna means of said array to said transducer to provide an effective rotation in which said antenna means comprise directive antenna units each having a directive radiation pattern and means connected to said coupling means for sequentially controlling the radiation of said antenna unit so that the radiation pattern of each unit moving along the circumference of a circle and the center of said circle coincide with the center of said circular array, said antenna means comprising antenna elements producing a substantially cardioidal pattern, the separation of any two adjacent antenna elements being equal to M4 where )t is equal to the wavelength at the operating frequency, and means to alternately couple said transducer from one of said adjacent antennas to the other to effectuate reversal of the cardioid pattern before the next two adjacent antennas are coupled.

2. A directional radiant acting circuit in a form of a circular array of antenna means, comprising a transducer, and means for cyclically coupling adjacent antenna means of said array to said transducer to provide an elfective rotation in which said antenna means comprise directive antenna units each having a directive radiation pattern and means connected to said coupling means for sequentially controlling the radiation of said antenna unit so that the radiation pattern of each unit moving along the circumference of a circle and the center of said circle coincide with the center of said circular array, said antenna means comprising two adjacent antennas, and said coupling means comprising means for effectively coupling two adjacent antennas whereby a cardioidal pattern is produced, and means to alternately couple said transducer from one of said adjacent antennas to the other to effectuate reversal of the cardioid pattern before the next two adjacent antennas are coupled.

3. A directional radiant acting circuit in a form of a circular array of antenna means, comprising a transducer, and means for cyclically coupling adjacent antenna means of said array to said transducer to provide an effective rotation in which said antenna means comprise directive antenna units each having a directive radiation pattern and means connected to said coupling means for sequentially controlling the radiation of said antenna unit so that the radiation pattern of each unit moving along the circumference of a circle and the center of said circle coincide with the center of said circular array, said antenna means comprising two adjacent antennas, and the means for cyclically coupling the antennas to said transducer operates in a predetermined direction of rotation, and further including means for connecting each antenna to its adjacent antenna in said predetermined direction of rotation, and means to alternately couple said transducer from one of said adjacent antennas to the other to effectuate reversal of the cardioid pattern before the next two adjacent antennas are coupled.

4. A directional radiant acting circuit in a form of a circular array of antenna means, comprising a transducer, and means for cyclically coupling adjacent antenna means of said array to said transducer to provide an effective rotation in which said antenna means comprise directive antenna units each having a directive radiation pattern and means connected to said coupling means for se quentially controlling the radiation of said antenna unit so that the radiation pattern of each unit moving along the circumference of a circle and the center of said circle coincide with the center of said circular array, said antenna means comprising an inner and outer circular array of antennas, the number of said antennas of said outer array being equal to the number of antennas in said inner array, and said inner array of antennas being positioned to act as a reflector to the nearest antennas of said outer array to produce a directional radiation pattern.

5. A directional radiant acting circuit as in claim 3, wherein said means for connecting each antenna to its adajcent antenna comprises a conductor having an electrical length equal to the spacing between adjacent antennas.

6. A directional radiant acting circuit as claimed in 1 claim 5, wherein the electrical length of said conductor is equal to M4, wherein A is equal to the wavelength at the operating frequency.

References Cited in the file of this patent UNITED STATES PATENTS 2,411,518 Busignies Nov. 26, 1946 2,444,425 Busignies July 6, 1948 10 2,502,131 Earp Mar. 28, 1950 2,962,715 Byatt Nov. 29, 1960 OTHER REFERENCES Proceedings of the IRE, December 1953, pages 1750- 5 1755. Copy in Scientific Library. 

4. A DIRECTIONAL RADIANT ACTING CIRCUIT IN A FORM OF A CIRCULAR ARRAY OF ANTENNA MEANS, COMPRISING A TRANSDUCER, AND MEANS FOR CYCLICALLY COUPLING ADJACENT ANTENNA MEANS OF SAID ARRAY TO SAID TRANSDUCER TO PROVIDE AN EFFECTIVE ROTATION IN WHICH SAID ANTENNA MEANS COMPRISE DIRECTIVE ANTENNA UNITS EACH HAVING A DIRECTIVE RADIATION PATTERN AND MEANS CONNECTED TO SAID COUPLING MEANS FOR SEQUENTIALLY CONTROLLING THE RADIATION OF SAID ANTENNA UNIT SO THAT THE RADIATION PATTERN OF EACH UNIT MOVING ALONG THE CIRCUMFERENCE OF A CIRCLE AND THE CENTER OF SAID CIRCLE COINCIDE WITH THE CENTER OF SAID CIRCULAR ARRAY, SAID ANTENNA MEANS COMPRISING AN INNER AND OUTER CIRCULAR ARRAY OF ANTENNAS, THE NUMBER OF SAID ANTENNAS OF SAID OUTER ARRAY BEING EQUAL TO THE NUMBER OF ANTENNAS IN SAID INNER ARRAY, AND SAID INNER ARRAY OF ANTENNAS BEING POSITIONED TO ACT AS A REFLECTOR TO THE NEAREST ANTENNAS OF SAID OUTER ARRAY TO PRODUCE A DIRECTIONAL RADIATION PATTERN. 